Question

var friends = ["Miha", "Artur", "Karen", "zollex"];
var len = friends.length;
var friend = 0;
var msg = '';
var i;
for (i = 0; i <len; i++){ 
  friend = (i + 1);
  msg+= "Friend number " + friend + ":";
  msg+=friends[i] + "<br />";
  document.write(msg);
}

我上面写的代码如下。结果如下：

朋友1：Miha
朋友1：Miha
朋友2：阿图尔朋友1：Miha
朋友2：阿图尔朋友3：凯伦
朋友1：Miha
朋友2：阿图尔朋友3：凯伦
朋友4：zollex

虽然应该只有4个朋友。我真的好奇为什么document.write多次重复同名。

Answer 1

因为您在每次迭代时使用+ =构建字符串，并且您不会在每次迭代时重置它。

msg += "Friend number " + friend + ":";
    ^^
msg += friends[i] + "<br />";
    ^^

将document.write移出for循环或在每次迭代时将msg设置为空。

var friends = ["Miha", "Artur", "Karen", "zollex"];
var len = friends.length;
var friend = 0;
var msg = '';
var i;
for (i = 0; i <len; i++){ 
  friend = (i + 1);
  msg += "Friend number " + friend + ":";
  msg += friends[i] + "<br />";
}
document.write(msg);

Answer 2

for (i = 0; i <len; i++){ 
  msg = '';
  friend = (i + 1);
  msg+= "Friend number " + friend + ":";
  msg+=friends[i] + "<br />";
  document.write(msg);
}

你正在覆盖每个循环上的msg变量，而你应该在每个循环上清除它！

javascript简单循环

2 个答案: